The primary objective of this contract is to titrate a pathogenic HIV455NC virus stock administered by a mucosal route to chimpanzees. The components of this objective include the determination of whether a whole blood 'swarm' of this strain of HV can cause infection at any dose when given rectally and determine of the ID50 titer for the virus stock. Following exposure, animals will be monitored for infection by serial PCR or branched-DNA viral load measurements plus a variety of immune function assays (antibodies, CTL's, CD4+ cells, CD8+ suppressor cell activity, etc.). These responses will be measured both locally and systematically to map the early events following exposure. The endpoint measurement will be the development of clinical AIDS in infected animals.